(1) Field of the Invention
This invention pertains to the conversion of hydrocarbons, especially the dehydrogenation of dehydrogenatable hydrocarbons, in the presence of a catalyst composite. This invention also pertains to a new catalyst composite and a method of making it.
Dehydrogenating hydrocarbons is an important commercial hydrocarbon conversion process because of the great demand for dehydrogenated hydrocarbons for the manufacture of various chemical products such as detergents, high octane gasolines, pharmaceutical products, plastics, synthetic rubbers, and other products well-known to those skilled in the art. One example of this process is dehydrogenating isobutane to produce isobutylene which can be polymerized to provide tackifying agents for adhesives, viscosity-index additives for motor oils and impact-resistant and anti-oxidant additives for plastics.
(2) Description of the Prior Art
It is well-known to catalyze the conversion of hydrocarbons with solid catalysts comprising platinum group metals. For example, U.S. Pat. Nos. 2,479,109 and 2,479,110 disclose a catalyst comprising platinum on alumina with combined halogen for catalyzing reforming, hydrogenating, hydrocracking, oxidizing and dehydrogenating reactions. The term "reforming" in these patents means simultaneously dehydrogenating, isomerizing, cyclizing and cracking a gasoline feedstock. The combined halogen component of this catalyst contributes to a controlled type of cracking activity. The halogen content is preferably maintained below about 8 weight % of the alumina to avoid excessive side reactions, including cracking reactions, which result in excessive gas formation and low liquid volume yield of reformed products. These patents do not disclose utilizing an alkali or alkaline earth component.
U.S. Pat. No. 2,602,772 discloses converting hydrocarbons, especially reforming and hydrocracking hydrocarbons, with a catalyst comprising platinum, not more than 1 weight % of an oxide of an alkaline earth metal or magnesium and from about 0.1 to about 8 weight % combined halogen on alumina. According to this patent catalysts containing an alkaline earth metal or magnesium oxide produced less carbon, or coke, after 3 days of reforming operations. The halogen content for catalysts of this patent is from 0.3 to 3 weight %, preferably between 0.6 and 2.3 weight %. This patent does not disclose utilizing a Group IVA component.
U.S. Pat. No. 2,930,763 discloses a two-step process for reforming hydrocarbons. In the first step a hydrocarbon fraction containing unsaturated compounds and/or nitrogen, sulfur or oxygen compounds is contacted with hydrogen in the presence of a catalyst comprising platinum and an alkali metal component on alumina to hydrogenate and saturate the unsaturated compounds and/or reduce the nitrogen, sulfur or oxygen content of the hydrocarbon fraction. In the second step of this process the treated hydrocarbon fraction from the first step is contacted at reforming conditions with a conventional reforming catalyst comprising platinum and combined halogen on alumina. Optionally the catalyst utilized in the first step may contain halogen. A catalyst consisting essentially of alumina, from about 0.01% to about 1% by weight of platinum, from about 0.1% to about 1% by weight of combined halogen, and from about 0.01% to about 1% by weight of an alkali metal is recited in claim 2 of this patent. This patent also does not disclose utilizing a Group IVA component.
U.S. Pat. No. 3,531,543 discloses dehydrogenating hydrocarbons with a catalyst comprising platinum, tin and neutralized metal oxide carrier. The preferred carriers are oxide materials whose intrinsic acidity is substantially neutralized by an alkali or alkaline earth metal component. Pure alumina, for example, has such intrinsic acidity. (cf. Pines and Haag, Journal of the American Chemical Society, 82, 2471 (1960)). For example, alumina catalyzed the skeletal isomerization of olefins, dehydrates alcohols and strongly chemisorbs amines. Also, with increasing amounts of alkali present there is a parallel decrease in these acidic alumina properties. Preferably the carrier of this patent is a non-acidic lithiated alumina. Preferably, the catalysts of this patent are prepared from halogen-free compounds. Compounds containing halogen may be used to manufacture the catalyst provided the halogen residue is efficiently removed from the final catalyst composite.
U.S. Pat. No. 3,745,112 discloses a catalyst for reforming hydrocarbons which comprises a platinum group component, a tin component and a halogen component with a porous carrier material. This patent discloses also that a platinum-tin-alkali or alkaline earth composite is a particularly effective catalyst for dehydrogenating hydrocarbons. In the dehydrogenation catalyst composite of this patent wherein the alkali or alkaline earth component is added the amount of halogen,if not entirely eliminated, is minimized in order to minimize or neutralize the acidic functions of the alumina and halogen components which tend to promote hydrocarbon cracking and isomerization side reactions which are not desired in commercial dehydrogenation processes.
U.S. Pat. No. 3,892,657 discloses that indium is a good promoter for platinum group-containing catalysts when the atomic ratio of indium to platinum is from about 0.1:1 to about 1:1. This patent discloses also that a Group IVA component selected from the group of germanium, tin, and lead can be added to the acidic form of the indium-containing catalysts for reforming applications. The acidic form of this catalyst, then, comprises a platinum group component, a Group IVA component, an indium component, a halogen component and a porous carrier material. The acidic catalyst contains up to about 3.5 weight % halogen for reforming applications and up to about 10 weight % halogen for isomerization and cracking applications. In the dehydrogenation catalyst of this patent wherein the alkali or alkaline earth component is added, however, the halogen content is maintained at the lowest possible value (about 0.1 weight %).
U.S. Pat. No. 3,909,451 discloses a new method for making a dehydrogenation catalyst comprising a platinum component, a tin component and an alkali or alkaline earth component. In Example V this patent discloses a platinum, tin and potassium composition comprising less than 0.2 weight % combined chloride.
U.S. Pat. Nos. 4,329,258 and 4,363,721 disclose a catalyst comprising a platinum group metal, tin, an alkali or alkaline earth metal and combined halogen element with a refractory oxidemineral carrier. The atomic ratio of alkali or alkaline earth metal to platinum group metal for catalysts of these patents is from 0.2 to 10. The patentees discovered that parts-per-million quantities of alkali or alkaline earth component added to catalyst containing a platinum group metal, tin and halogen helped increase the C.sub.5 + yield in a reforming process.
British Pat. No. 1 499 297 discloses a dehydrogenation catalyst comprising platinum, at least one of the elements gallium, indium and thallium, and an alkali metal, especially lithium or potassium, with alumina as the carrier material. The catalysts of this patent also contain a halogen in an amount of from 0.01 to 0.1 weight %. The halogen content is purposely reduced to within this low weight % range in order to increase the selectivity and stability of the catalyst.
In the prior art dehydrogenation catalysts acknowledged above comprising a platinum group component, a Group IVA component and an alkali or alkaline earth component wherein the atomic ratio of the alkali or alkaline earth component to the platinum group component is more than 10, then, the halogen component has been eliminated completely or otherwise maintained at the lowest possible level, generally less than 0.1 weight %, and always less than 0.2 weight %, calculated on an elemental basis.
Surprisingly, we discovered that incorporating more halogen component than was previously present in these types of dehydrogenation catalysts provided catalysts with improved activity and selectivity characteristics.